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real_python/README.md

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+# Real Python AsyncIO Walkthrough
+
+https://realpython.com/async-io-python/
+
+## Rules of Async Coroutines
+
+```python
+async def f(x):
+    y = await z(x)  # OK - `await` and `return` allowed in coroutines
+    return y
+
+async def g(x):
+    yield x  # OK - this is an async generator
+
+async def m(x):
+    yield from gen(x)  # No - SyntaxError
+
+def m(x):
+    y = await z(x)  # Still no - SyntaxError (no `async def` here)
+    return y
+```
+
+An awaitable object is either (1) another coroutine or (2) an object defining an .__await__() dunder method that returns an iterator.

real_python/countasync.py

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+#!/usr/bin/env python3
+# countasync.py
+
+import asyncio
+
+
+async def count():
+    print("One")
+    await asyncio.sleep(1)
+    print("Two")
+
+
+async def main():
+    await asyncio.gather(count(), count(), count())
+
+
+if __name__ == "__main__":
+    import time
+
+    s = time.perf_counter()
+    asyncio.run(main())
+    elapsed = time.perf_counter() - s
+    print(f"{__file__} executed in {elapsed:0.2f} seconds.")

real_python/countsync.py

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+#!/usr/bin/env python3
+# countsync.py
+
+import time
+
+
+def count():
+    print("One")
+    time.sleep(1)
+    print("Two")
+
+
+def main():
+    for _ in range(3):
+        count()
+
+
+if __name__ == "__main__":
+    s = time.perf_counter()
+    main()
+    elapsed = time.perf_counter() - s
+    print(f"{__file__} executed in {elapsed:0.2f} seconds.")

real_python/randasync.py

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+#!/usr/bin/env python3
+# rand.py
+
+import asyncio
+import random
+
+# ANSI colors
+c = (
+    "\033[0m",  # End of color
+    "\033[36m",  # Cyan
+    "\033[91m",  # Red
+    "\033[35m",  # Magenta
+)
+
+
+async def makerandom(idx: int, threshold: int = 6) -> int:
+    print(c[idx + 1] + f"Initiated makerandom({idx}).")
+    i = random.randint(0, 10)
+    while i <= threshold:
+        print(c[idx + 1] + f"makerandom({idx}) == {i} too low; retrying.")
+        await asyncio.sleep(idx + 1)
+        i = random.randint(0, 10)
+    print(c[idx + 1] + f"---> Finished: makerandom({idx}) == {i}" + c[0])
+    return i
+
+
+async def main():
+    res = await asyncio.gather(*(makerandom(i, 10 - i - 1) for i in range(3)))
+    return res
+
+
+if __name__ == "__main__":
+    random.seed(444)
+    r1, r2, r3 = asyncio.run(main())
+    print()
+    print(f"r1: {r1}, r2: {r2}, r3: {r3}")